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Mr. W. S. Savory on the Structure of the [Mar. 18, 



present throughout a granular aspect. I have almost invariably observed, 

 too, a relation between the distinctness of the nucleus and of the cell-wall. 

 When the nucleus is well defined, the cell-wall is strongly marked ; when 

 one is confused, the other is usually fainter. This, however, does not 

 apply to colour ; on the contrary, when the nucleus is least coloured it 

 contrasts most strongly with the surrounding cell. As a rule, the wall 

 of the cell is more strongly marked than the nucleus. 



It will of course be said that the nuclei are present all the while, but 

 are at first concealed by the surrounding substance — the contents of the 

 cell. Thus the fact has been accounted for, that the nuclei are not so 

 obvious at first as they subsequently become. But I think a careful com- 

 parison of cells will show that those in which a nucleus may be traced are 

 not more transparent than others which are structureless ; and, moreover, 

 when one cell overlaps another, the lower one is seen through the upper 

 clearly enough to show that the substance of these cells is sufficiently 

 transparent to allow of a nucleus being discerned if it exists. When a 

 nucleus is fully formed, it hides that portion of the outline of a cell which 

 lies beneath it. How is it, then, if the nucleus is present from the first, 

 that the portion of the cell over which it subsequently appears is, for 

 a while, plainly seen ? 



The success of the observation is of course influenced by numerous cir- 

 cumstances. The rate at which the nuclei form in the corpuscles varies in 

 different animals. I have usually found that in the common frog they are 

 more prone to form than in many other animals — quicker than in most 

 fishes, or even than in some birds. But this does not seem always to 

 depend upon their larger size; for in the common newt the cells, which are 

 larger than those of the frog, remain, as I have noticed, for a longer period 

 without any appearance of nuclei. But even in the frog it can be satis- 

 factorily demonstrated that the corpuscle is structureless. 



I have found, too, that the observation succeeds best with the blood of 

 animals which are healthy and vigorous. Thus the first observations upon 

 fresh animals are usually the most satisfactory. After they have been 

 repeatedly wounded or have lost much blood, the cells are more prone 

 to undergo the changes which result in the production of nuclei. 



Again, the formation of nuclei may be hastened, and their appearance 

 rendered more distinct at last, by various reagents. Acids and many ether 

 reagents are well known to have this effect. The addition of a small 

 quantity of water acts in the same way, but less energetically. It hastens 

 the appearance of an indistinct nucleus, but interferes with the formation 

 of a well-defined mass, so that, after the addition of water, neither the 

 outline of the cell nor of the nucleus becomes so strongly marked as it often 

 does without it. Exposure to air also promotes their formation ; indeed, as 

 a rule, the nuclei form best under simple exposure. Any disturbance of 

 the drop, as by moving the point of a needle in it, certainly hastens the 

 change; and perhaps it is influenced by temperature. 



